The work done in these experiments was on a stationary-bicycle in the calorimeter, and the heat equivalent was calculated from measurements made by an ergometer attached to the bicycle. We are not concerned here with details, but simply with the general question of the influence of muscular work upon the energy exchange of the body. We note that the work of the day periods, 7 A. m. to 7 P. M., resulted, in the several cases brought together under the average figures, in an increased heat production amounting to more than 100 per -cent. Further, we observe that in the body, as in all machines, only a fraction of the energy liberated by the accelerated chemical decomposition, or oxidation, was manifested as mechancial work, the larger part by far being heat eliminated and lost. Thus, Zuntz has found that, in man, about 35 per cent of the extra energy of the food used in connection with external muscular work is available for That work. This, however, shows a noticeably higher degree of efficiencey than is genetally obtaimable by the best steam or oil engines. Lastly, attention may be called to the fact that after the work of the day was finished at 7 P. M., the next period of six hours still showed an accelerated metabolism, as contrasted with what took place during absolute rest.

As bearing upon the exchange of matter in the body in connection with muscular work, and as showing the relationship which exists here between energy exchange and exchange of matter, we may quote a few data relating to the elimination of carbon dioxide; remembering that this substance represents particularly the final oxidation product in the body of carbonaceous materials, such as fat and carbohydrate. The following data, taken from At water and Benedict,1 being results of experiments upon the subject "J. C. W.," are of value as showing the variations in output of carbon dioxide that may be expected under the conditions described:

In considering these figures bearing on the output of carbon dioxide under the conditions specified, we note at once a correspondence with the total energy exchange, as indicated in the preceding table. As previously stated, we are at present dealing simply with generalities, and the important point to be observed here is that muscular work - 7 a.m to 7 P. M. - in the work experiments, increases enormously the output of carbon dioxide. We see clearly emphasized a connection between the total energy exchange of the body, as expressed in calories or heat units, and the oxidation of carbonaceous material, of which carbon dioxide is the natural oxidation product. We note that on the cessation of work -

1 Loc, cit., pp. 130 and 131.

7 p. m. to 7 a. m. - the output of carbon dioxide tends to drop back to the level characteristic of the corresponding period in rest, with or without food. In the experiment with "extra severe muscular work," the results are different simply because here the subject worked sixteen houre, necessitating a portion of the work being done at night-time. Finally, it should be mentioned that the differences in output of carbon dioxide in these experiments are somewhat greater than in many experiments of this type, although all show the same general characteristics. This may be explained, as stated by the authors from whom the data are taken, "by the fact that J. C. W. was a larger and heavier man than any of the others; that the differences in diet were wider, and that the amounts of external muscular work were larger in these experiments than in those with the other subjects."

If we pass from experiments of this type, conducted in a calorimeter, to those cases where competitive trials of endurance are held by trained athletes, i. e., where external muscular activity is pushed to the extreme limit, we then see even more strikingly displayed the effect of work in increasing the energy exchange of the body. One of the best illustrations of this type of experiment is to be found in the observations made in connection with the six-day bicycle race held in New York City, at the Madison Square Garden, in

Deember, 1898.1 The observations in question were made upon three of the athletes, one of whom withdrew early in the fourth day, while the others continued until the close of the race - 142 consecutive hours - winning the first and fourth places, respectively. The following table gives the computation of energy of the material metabolized, exclusive of body-fat lost:

Miller, the winner of the race, who averaged a daily energy exchange of 4820 calories, rode 2007 miles during the week, and finished the race without physical or mental weakness resulting from the fatigue and strain. During the first five days, he rode about 21 hours a day and slept only 1 hour. Albert, who weighed a few pounds less than Miller, covered 1822 miles in 109 hours, with an average daily exchange of 6074 calories. We may add a table (on the following page) showing the balance of income and outgo of nitrogen in these three subjects, as being of general interest in this connection. The figures given are averages per day.

The special significance of these data, as bearing upon the topic under discussion, is that apparently all three of the subjects were drawing in a measure upon their body material. As stated by Atwater and Sherman, Pilkington lost per day 5.1 grams of nitrogen; that is to say, the total nitrogen ex-

1 See W. O. At water and H. C. Sherman i The effect of terere and prolonged mucular work on food conaumption, digeition, and metabolism. Bulletin No. 98, Office of Experiment Station., U. S. Department of Agriculture.

creted exceeded the total nitrogen of the food by 5.1 grams per day, corresponding to 33 grama of proteid, which must have been drawn from the supply in the body. If we assume that lean flesh contains 25 per cent of proteid. this would mean about 4¾ ounces per day. The other two subjects, Miller and Albert, lost from the body per day 8.6 grams and 7.1 grains respectively of nitrogen, which would imply a loss of about 54 grams and 44 grams of body proteid respectively, or 8 ounces and 6¼ ounces of lean flesh per day It is evident, therefore, that none of the three subjects consumed sufficient food to avoid loss of body proteid, under the existing conditions of muscular activity. Indeed, it may he noted in Miller's case that the average fuel value of the food per day was 4770 calories, while the average expenditure of energy per day was 4820 calories. We should naturally expect, however, that any small deficiency in fuel value would be made good by a call upon body fat. "Why the body should use its own substance under such circumstances is a question which at present cannot be satisfactorily answered. The fact that such was the case, each of the contestants who finished the race consuming during the period body protein equivalent to 2 or 3 pounds of lean flesh, and that no injury resulted therefrom, would seem to indicate that these men had stores of protein which could be metabolized to aid in meeting the demands put upon the body by the severe exertion, without robbing any of the working parte, and at the same time relieving the system of a part of the labor of digestion. Possibly, the ability to carry such a store of available protein is one of the factors which make for physcial"1 This possibility we shall have occasion to discuss in another connection. At present, the facts presented are to be accepted as accentuating the general law that the energy exchange of the body, everything else being equal, is increased proportionally to increase in the extent of external muscular activity. It may be noted that Albert, who did considerably less work than Miller, showed a much larger exchange of energy than the latter athlete. This, however, is to be connected with the fact that his fuel intake was 1300 calories larger per day than Miller's; in other words, the conditions were not equal. This fact also calls to mind the observations of Schnyder,2 who, studying the relationship between muscular activity and the production of carbon dioxide, maintained that the quantity of this excretory product formed depends less upon the amount of work accomplished than upon the intensity of the exertion; efficiency in muscular work varying greatly with the condition of the subject, and his familiarity with the particular task involved.